Plow point



May 1, 1945. H. D. BROWN ET Al.

PLOW PO INT Filed Feb. 26, 1944 2 Sheets-Sheet l BY iq-Lu. um; V ATTORNEY May1,1945. H. QBROWN m1 v2,?1'1013 PLOW POINT Filed Feb. 26, 1944 2 Sheets-Sheet 2 Cros.; Sectl'n Zine 76 i INVENTORS A TT RNEY Patented May 1, 1945 PLow POINT Howard D. Brown, Westfield, and Albert Edward Freeman, South Orange, N. J., assignors to American Telephone and Telegraph Company.. a corporation of New York Application February 26, 1944,Serial No. 523,992

(Creez- 33) 6,0lams.

This invention relates to plows and more particularly to improvements in points to be used in` the plowshare `assembly of a rooter type plow.

A rooter type plow is one which is used for extremely rough or heavy work, such as tearing up a road bed or making a preliminary plow cut in front of the path of another plow such as one utilized to `lay a cable in a communication system. The plow point of the rooter plowshare assembly to perform ythe rough work required of it must be of heavy strong metal but nevertheless it will be worn away due to the rugged nature of the work involved. The wearing awayof `the cutting edge of a plow point will ordinarily cause it to become progressively duller and hence require greater power to operate the plow. Accordingly, it would be desirable to maintain the cutting edge of the point as near as possible at its original degree of sharpness. In view of the foregoing, one of the features of the arrangements of the invention is that the point of the plowshare assembly is designed to be self-sharpening while itis being worn away. This is accomplished by making the shape of the point such that while the metal is worn away from the cutting edge the bearing area on the bottom of the point which has a direct relation to the sharpness of the point remains relatively constant throughout the designed service life of the point. Another feature of the invention is that the foregoing constancy of bearing area is achieved without materially reducing the effective strength of the point during the time its cutting edge is being worn away. Other objects and features of the invention will appear more fully from the detailed description thereof hereinafter given.

The invention may be more fully understood from the following description together with the accompanying drawings in the` Figures 1 to 10` of which the invention is illustrated. Figure 1 is a View of the plow point` of .the invention looking at one side thereof and partially underneath it. Fig. 2 is a plan view of the` top of the plow point. Figs. 3 and 4 are views of certain typesof cantilever beams used in explanation of the theories involved. Figs. 5 and 6 are side views of portions of the plow point of the invention before and after it has been worn away. Figs. '7, 8 and 9 are sectionalviews` of portions 0f Figs. 5 and 6. Fig. l0 is a curve illustrating the degree of sharpness of the plow point as it is worn away. Similar referencecharacters have been` utilized to denote like parts in all of the iigures.l l As `chown in Figs. 1 and 2, thev plow point'of `increases toward the xed support. of beam will not necessarily break at point C, as

theinvention comprises a section with a flat top I rounded to a point which forms the cutting edge 2; The flat top section is integral with a second section 3 which might be bolted to a plowshare assembly. The underneath portion of the f front of the iflat top section near the cutting edge is hollowed out as shown. This would result in two side walls 4 and 5. In these side walls are provided two crescent-shaped holes 6 and l. When the section 3 is bolted to a plowshare assembly the portion of the flat top section near the cutting edge will form a type of cantilever beam.

In Figs. 3 and 4 are shown two types of cantilever beams. The bending or breaking moment on such beams is the load times distance. The resistance moment of the beam depends upon its depth at the xed support. This resistance moment must begreater than the bending moment in order to prevent failure of the beam. In Fig. 3 the cantilever beam ACEF which is rmly ailixedto the member 9 is of uniform depth throughout.` If theload on the beam ACEFis moved from point A to point B nearer the fixed support 9, the bending moment on beam ACEF will decrease. Accordingly, a beam such as BCGKshown by a shaded area would support the same load at point B that the beam ACEF would support at point A. In other words, with the load at point B a beam the size of BCGK would have the equivalent strength of the beam ACEF with the load ai; point A. In Fig. 4 is shown another type of cantilever beam ACJ attached to aiixed support I3. This type of beam is known, as a uniform strength beam and its depth This" type is the case ,with beam ACEF, but will probably shear atthe pointof load or break at any other point along the beam. In this type of beam the bendingor breaking moment decreases as the load is moved toward Vthe xedsupport I3. Accordingly, a beam such as BCH shown by a shaded area wouldisupport thesame load at point B that a beam ACJ would support at DOint A. In other words, with the load at point; B a beam the size of BCH would` `have the equivalentA strength of thebeam ACJ with the load at point A. `In `a like manner with the load at; point D a beam the: size of DCI would have the equivalent strength of a beam` ACJ with the load at pointA.

As heretofore` pointed out, it is desirable to maintain the cuttingl edge of the plow point of the invention as near as possible at its original degree of sharpness. Sharpness may be defined as thinness of edge. As the plow point of the invention is a relatively blunt instrument compared with a knife or razor blade its sharpness may be considered from the standpoint of the area of its cutting edge. As shown in Fig. 1 a portion of the front part of the plow point is hollowed out leaving a cutting edge 2 and two side or supporting walls 4 and 5. The purpose of hollowing out this portion is that the area of a part of the cutting edge 2, namely, that portion between side walls 4 and 5, will remain almost constant or at its original sharpness as the plow point Wears away. The purpose of leaving the two side walls 4 and 5 is to provide support for the cutting edge against load and to cause the point to resemble to a certain degree a cantilever beam of the uniform strength type such as is shown in Fig. 4. Accordingly, portions of the front areas of the two side walls must, as the plow point is being worn away, be added to the area of the cutting edge in determining the overall area or sharpness of the plow point at a given time. As the plow point wears away it will be seen that as the side walls increase in depth toward the fixed support the area of portions of the side walls contacting undisturbed earth will slowly increase and cause the plow point to become slightly duller. When the point is suiciently worn away so that the supporting feature of the side walls is no longer needed the arrangements of the invention provide for a decrease in that area of portions of the side walls which must be added to the area of the cutting edge and hence will cause the plow'point to .become sharper again. This will appear more fully from the following discussion of Figs. 5 to 9.

In Fig. 5 is shown a side View of the plow point of the invention. The dotted line I4 and the line A-C show the angle of the plow point as it enters the earth. The dotted lines I5, I6 and I1, together with the line A-C, show the shape of the plow point as it progresses through the earth and after its cutting edge has been partially worn away. It will be seen that the bearing area of the plow point at line I4 will only be the length times the width of the cutting edge 2 and hence, at this point the plow point will have the maximum desired degree of sharpness. When the plow point is at the dotted line I4 the cantilever arm formed by the plow point may be compared to the cantilever arm shown by the figure ACJ of Fig. 4. As the plow point progresses through the earth and is worn away, as indicated by dotted line I5, it will become slightly less sharp because to the area of the cutting edge 2 must be added the area of portions of the front of the side walls 4 and 5. Fig. '7 is a cross-section of the plow point as worn away to the dotted line I5. It will be seen that the total area to be considered in determining the sharpness of the plow point at the time it has been worn down to a degree indicated by the dotted line I5 will be the shaded area of the edge 2 plus the shaded area of a. part of the front portions of side walls 4 and 5 shown in Fig. 7. This area of portions of the side walls 4 and 5 to be added to the area of the cutting edge 2 would be determined by their width times the length QR on dotted line I5`of Fig. 5. When the plow point has been worn away to a degree indicated by the dotted line I6, the support afforded to the plow point by that portion of the side wall. 5 to the left of line I6 will, because of the crescent-shaped hole 6, be gone. However, at this point the remainder of the plow point may now be compared to the cantilever arm shown by the iigure DCI of Fig. 4. As heretofore pointed out with respect to Fig. 4, a beam such as DCI will support at point D a load equal to the load which could be supported at point A by the beam ACJ. Accordingly, no need will exist for the extra support afforded by that portion of the side wall 5 to the left of the dotted line I6. At this point, namely, in the condition shown by the dotted line I6, the plow will be somewhat duller than before due to the fact that the area of portions of the side walls to be added to the area of the cutting edge is increased. This condition is shown in Fig. 8 which is a cross-section of the plow pointworn away to the dotted line I6. The area of portions of the side walls 4 and 5 now to be added to the area of the cutting 'edge 2 would be determined by their width times the length LP on dotted line I6 of Fig. 5. However, from this point on, the cutting edge of the plow point will commence to grow sharper. For example, when the plow point has worn away to a degree indicated by the dotted line I'I, it will have the shape indicated in Fig. 6. At this point the remainder of the plow point may be compared to the cantilever arm shown by the gure BCH of Fig. 4. Due to the presence of the crescentshaped holes 6 and 1 the bearing area of certain portions of the front of side walls 4 and 5 will now be eliminated and the area nOW to be added to the cutting edge diminished. This is because the bearing area of the portions of the side walls 5 and 6 which must be added to the area of the cutting edge isnow represented by their width times the distance MN on dotted line I'I of Fig. 5. This area would be less than the area of the side arms 4 and 5 when their length was as indicated as LP on line I6. This condition is illustrated in Fig. 9 which is a cross-section of the plow point at line II. This will cause the plow point to become sharper again without causing any sacrice in its strength with respect to its load because as heretofore pointed out a beam such as BCH will support at point B a load equal to the load which may be supported at point A by the beam ACJ.

In Fig. 10 is shown a curve illustrating variations in the sharpness of the plow point of the invention as it is worn away and also the degree to which it is self sharpening. In Fig. 10 the ordinates represent the bearing surface (or sharpness) of the plow point in square inches and the abscissae represent the wearing away of the plow point in inches. The curve represented by the line joining points 30, 3l, 32, 33, 34, 35 and 36 represents how the sharpness of the plow point of the invention varies as it is worn away. That portion of the curve between points 30 and 3l showsl the degree of sharpness of the plow point at the dotted lino I4 of Fig. 5 or when it enters the earth. This is the maximum degree of sharpness of the plow point. When the plow point is worn away to the degree illustrated by dotted line I5 of Fig. 5 its sharpness will be represented by point 32 of the curve. In other Words the plow point as hereton fore pointed out has become somewhat duller. As the plow point is further worn away it becomes still duller until it is worn down to the degree illustrated by the dotted line I6 of Fig. 5. At this point its sharpness is illustrated by point 33 of the curve. From now on the plow point as it is worn away will become progressively sharper. When it is worn down to the degree shown by dotted line I1 of Figs..5 and 6 its sharpness will be illustrated by point 34 on the curve. From this point on the plow point becomes only slightly duller until the end of its designed service life is approached, at which point the curve rapidly rises as shown by that portion of the curve from points 35 to 36. Because of theyshape and positioning of the crescent-shaped holes yl and `l it often happens that when the plow point becomes worn away to a degree between the dotted lines i6 to Il of Fig. 5, or as above shown in Fig. 6, the lower portion of the side walls 4 and '5 below the crescentshaped openings ii and 'l will be' sheared olif by hitting extremelyhard ground, a rock or other obstruction. When this happens the sharpness of the plow point will, because of this decrease in the bearing area of the side walls 4 and 5, be illustrated by the dotted line curve connecting points 33, 31, 38, 39 and 4E). Under such conditions the plow point will be restored practically to its original degree of sharpness.

As pointed out heretofore a portion of the front l part of the plow point is hollowed out leaving two side or supporting walls d and 5. This is an important feature of the invention. VIf this were not done and the point was solid in width with respect to its constantly increasing depth, its sharpness variation as it was being worn away would be represented by the dotted curve at the top of Fig. l connecting point 3U directly with point 36 If the plow point of the invention was hollowed out as shown and the crescent-shaped holes '6 and l were omitted, its sharpness variation as it was worn away would be represented by the curve joining points 30, 3l, 32, 33 and 4 I. e

From the foregoing it will be seen that the hollowing out of the plow point ofthe invention to form a cutting edge and two side or supporting walls has certain advantages. That portion of the cutting edge of the plow point between the two side walls will remain at its original degree of sharpness as the plow point is worn away and hence the point will remain sharper than if it was solid in width with a constantly increasing depth. The two side walls afford strength to the point and cause it to resemble a cantilever beam of the uniform strength type which will not be ma'- terially weakened with respect to load as it is worn away. Furthermore by providing the two side walls with the described crescent-shaped holes the plow point of the invention is self sharpening as it is worn away. vWhile the device of the invention has been described as embodied in a certain specific form which is `deemed desirable it is understood that it is capable of embodiment in many and other forms without departing from the spirit of the invention as defined by the appended claims.V

What is claimed is:

l. A plow point so formed `that it resembles a cantilever beam of the uniform strength type with its free end hollowed out to leave a cutting edge and two side or supporting walls which gradually increase in depth in the direction of the beams fixed support, each of said side aperture therein.

2. A plow point so formed that it resembles a walls having an cantilever beam of the uniform strength type with its free end hollowed out to leave a cutting edge and two side or supporting walls which gradually increase in depth in the direction of the beams nxed support, `each of said side walls having an aperture therein, opposite sides of said apertures being concave and convex, the concave sides being nearer the load side of the beam.

3. A plow point so formed that it resembles a cantilever beam of the uniform strength type with its free end hollowed out to leave a cutting edge and two side or supporting walls which gradually increase in depth in the direction of the beams xed support, each of said side walls having an aperture therein, said aperture being so shaped and positioned that after the plow point is worn away so that its bearing area reaches said apertures said bearing area will be gradually reduced and the plow point will become sharper.

4. A plow point so formed that it resembles a Icantilever beam of the uniform strength type with its free end hollowed out to leave a cutting edge and two side'or supporting walls which gradually increase in depth in the direction of the beams xed support whereby as the plow point is first worn away that area of portions of the front of the side walls to be added to the area of the cutting e edge of the beam to determine its sharpness will be increased and the beam or plow point will become duller, each of said side walls having an aperture therein, Vsaid apertures being so shaped and positioned that after the side walls are Worn away to the point where the apertures are positioned the area of portions of the front of the side walls to be added to the area of the cutting edge of the beam will, as the beam is further worn away, be decreased and the beam or plow point will become sharper. i .5. A plow point so formed that it resembles a cantilever beam of the uniform strength type with its free end hollowed out to leave a cutting edge and tWoside or supporting walls which gradually increase in depth in the direction of the beams fixed support, crescent-shaped apertures in each of said side walls, said apertures being so positioned that when said cutting edge and side walls are worn away to the point where said apertures are positioned and the remaining part of said side walls sheared oif by the operation of the plow point the cutting edge will be restored approximately to its original degree of sharpness. u

6. A plow point so formed that it resembles a cantilever beam of the uniform strength type with its free end hollowed out to leave a cutting edge and two side or supporting walls which gradually increase in depth in the direction of the beams xed support, crescent-shaped apertures in each of said side walls, said apertures being so positioned that the convex sides thereof will be close to the lower part of the cutting edge and the ends thereof will be close to the nxed support of the beam.

HOWARD D. BROWN. ALBERT EDWARD FREEMAN. 

